Shown in FIG. 1 is a turbomachine of the type with unducted propellers. It comprises, from upstream to downstream, in the air flow direction shown by the arrows F, a compressor 2, an annular combustion chamber 3, a high-pressure turbine 6, and two contra-rotating low-pressure turbines 8. Each low-pressure turbine 8 is integral with an external propeller 9, the two propellers being arranged coaxially one behind the other around a longitudinal axis A of the turbomachine 1 and each comprising a plurality of blades P regularly distributed around said axis.
To this end, each propeller is attached to a ring 10 conventionally comprising (FIG. 2) a generally polygonal annular rotor body 11 (known by the terminology polygonal ring), centered on the longitudinal axis A of the turbomachine and having a series of radial cylindrical housings 12, regularly distributed around the axis A, provide for receiving the propeller blades. Each housing 12 also receives a ring gear to which is attached the body of a plate designed to receive the root 14 of a blade P. This ring gear is mounted in rotation in the housing 12 that receives it, which makes it possible to adjust the angular orientation of the blade P.
To accomplish this, the inner surface of a housing 12 is machined and adjusted to constitute a hub which receives the ring gear and the bearing rings of different bearings interposed between the inner surface of said housing and said ring gear.
Documents FR 2 992 677, EP 2 586 701 and FR 2 953 487 describe examples of propeller rings comprising such cylindrical housings.
During operation, however, the outer rings of the bearings are severely loaded and wear rapidly. For example, the annular body 11 is subjected to very high tangential forces under the influence of centrifugal loads due in particular to its very large diameter (around 1600 mm) and, to a lesser extent, axial loads. The annular body 11 therefore has a tendency to elongate in the tangential direction. Now the bearing rings are generally sintered in zones subjected both to tangential deformations and to axial deformations. These deformations having different amplitudes, they induce ovalization of these bearing rings at the root 14 of the blades P, which is a source of friction and rapid wear for the rings.
Document GB 1 549 001 describes a propeller ring comprising a deformable bearing support designed to receive a bearing in a ring gear. To this end, the bearing support comprises a deformable seat surface in the ring gear having a spherical contour arranged to come into contact with the bearing when the ring gear is deformed. However, this deformation of the bearing support does not allow avoiding ovalization of the bearing rings at the root of the blades.